regexDuplicateCharacterClassCharacters

Reports duplicate characters in regular expression character classes.

✅ This rule is included in the ts logical and logicalStrict presets.

Disallows duplicate characters in regular expression character classes. When a character appears multiple times in a character class, only one occurrence is needed. Duplicates are often typing mistakes and can be safely removed.

Examples

Duplicate Characters

❌ Incorre

AEconsB0patteAE< =sp ansty="le--0:#5CA7E4;--1:#3A68">81<1/sp ansty="le--0:#82AAFF;--1:#3B61">B0[aa1<1/sp ansty="le--0:#D6DEEB;--1:#403F">5<3;d ivclassNa="meco">

44AEco61B0pat446<88F spans="tyle--0:#D9F5DD;--1:#11">1<111/ spans="tyle--0:#82AAFF;--1:#3B">61B<0[a] spans="tyle--0:#D9F5DD;--1:#11">1<111/ spans="tyle--0:#D6DEEB;--1:#40">3

Character Already in Range

❌ Incorre

AEconsB0patteAE< =sp ansty="le--0:#5CA7E4;--1:#3A68">81<1/sp ansty="le--0:#82AAFF;--1:#3B61">B0[a-z 1<1/sp ansty="le--0:#D6DEEB;--1:#403F">5<3;d ivclassNa="meco">

44AEco61B0pat446<88F spans="tyle--0:#D9F5DD;--1:#11">1<111/ spans="tyle--0:#82AAFF;--1:#3B">61B0[1<111/ spans="tyle--0:#D6DEEB;--1:#40">3

Duplicate Ranges

❌ Incorre

AEconsB0patteAE< =sp ansty="le--0:#5CA7E4;--1:#3A68">81<1/sp ansty="le--0:#82AAFF;--1:#3B61">B0[a-z a-1<1/sp ansty="le--0:#D6DEEB;--1:#403F">5<3;d ivclassNa="meco">

44AEco61B0pat446<88F spans="tyle--0:#D9F5DD;--1:#11">1<111/ spans="tyle--0:#82AAFF;--1:#3B">61B0[1<111/ spans="tyle--0:#D6DEEB;--1:#40">3

Options

This rule is not configurable.

When Not To Use It

If you are intentionally using duplicate characters for documentation purposes or have auto-generated patterns, you might prefer to disable this rule.

Further Reading

• MDN: Character class
• MDN: Regular expressions

Equivalents in Other Linters

• ESLint: regexp/no-dupe-characters-character-class